ethanol precipitation

im trying to extract DNA from mammalian cell line to b specific normal NP cell line. the problem is after adding absolute ethanol the white stringy thing (DNA) is visible but i could not manage to pellet it down even though i spun it at 14000rpm for 10 min... to overcome this i tried overnight incubation in -20 degree Celsius but i still could not pellet it down. what could be causing this problem? any solution / suggestion for this?